1. Field of the Invention
The present invention is concerned with a process for protection of a gas turbine from damage caused by pressure pulsations. The invention is additionally concerned with a control system for carrying out a protection process of this type.
2. Brief Description of the Related Art
During the operation of a gas turbine, pressure pulsations can occur, especially in a combustion chamber of the gas turbine, due to the combustion process. Phenomena of this type can occur in frequency ranges of 2 Hz to several kHz, and they are accordingly also referred to as humming, screeching, or in more general terms, flame instabilities. These pulsations, if they have high amplitudes or if they last too long, can cause serious damage to the structure or to individual components of the gas turbine, especially to its combustion chamber, thus shortening the life of the gas turbine. Furthermore, pulsations may signal malfunctions in the combustion reaction, which may be caused, for example, by fluctuations in the fuel and/or fresh-air supply or by abrupt load changes. In isolated cases the pulsations can also extinguish the combustion reaction or its flame, which will cause an explosive gas mixture to form.
Modern gas turbines are therefore equipped with a pulsation protection system, which, on one hand, detects the pressure pulsations that occur during the operation of the gas turbine, and which, on the other hand, triggers appropriate protective actions, such as shutting down the gas turbine, when specified trigger conditions occur, such as a sudden occurrence of pulsations with very high amplitudes, or the occurrence of medium-amplitude pulsations for an extended length of time. Measuring of the pressure pulsations may take place, for example, with the aid of an appropriate pressure sensor, with the aid of which a pulsation-time signal can be generated that correlates with the occurring pulsations. A “pulsation-time signal” in the present context is understood to mean a signal that represents the amplitudes of the pulsations (ordinate values) in dependence on the time (abscissa values). The pulsation-time signal that is determined in this manner can now be split using electronic or digital methods according to Tchebychev, or the like, into certain monitoring frequency bands, which can be analyzed and evaluated individually. In the process it may be practical to perform an averaging process within the respective monitoring frequency band.
A process of this type for protection of the gas turbine from damage caused by pressure pulsations, however, is relatively inaccurate in its operation. For safety reasons it is therefore possible that protective actions, for example an emergency shutdown of the gas turbine, may occur even though this may not yet actually be necessary. An unnecessarily caused shutdown of the gas turbine, however, involves high costs and losses of income.